Matthew 6:3

“But when thou dost alms, etc.] Do it so privately, and with so much secrecy, that, if it was possible, thou mightest not know it thyself, much less make it known to others: let not thy left hand know what thy right hand doth; acquaint not thy nearest and dearest friend with it; let not one that sits at thy left hand know what thou art doing with thy right hand; it is a proverbial and hyperbolical phrase, expressing the secrecy of the action. It is a Jewish canon f380, that “he that gives a gift to his friend out of love, may make it known, hqdxb al lba, “but not if it be by way of alms”.””

“But when thou doest alms, let not thy left hand know what thy right hand doeth--So far from making a display of it, dwell not on it even in thine own thoughts, lest it minister to spiritual pride.”

“Let not thy left hand know ... - This is a proverbial expression, signifying that the action should be done as secretly as possible. The Hebrews often attribute actions to members which properly belong to persons. The encouragement for performing our acts of charity in secret is that it will be pleasing to God; that he will see the act, however secret it may be, and will openly reward it. If the reward is not granted in this life, it will be in the life to come. In multitudes of cases, however, alms given to the poor are “lent to the Lord” Proverbs 19:17, and will be repaid in this life. Rarely, perhaps never, has it been found that the man who is liberal to the poor has ever suffered by it…”

“Let not thy left hand know what thy right hand doth - A proverbial expression for doing a thing secretly. Do it as secretly as is consistent, With the doing it at all. With the doing it in the most effectual manner. Matthew 6:5”

“let: Mat 8:4, Mat 9:30, Mat 12:19; Mar 1:44; Joh 7:4 Matthew 6:4”